A coffee warmer is a device used to keep a cup of coffee at a desired temperature for a longer period of time. It typically consists of a heating plate or warming surface that is placed under a cup of coffee to maintain its temperature. Some coffee warmers also have temperature control features to allow you to set the desired temperature for your coffee. The main purpose of a coffee warmer is to keep coffee at a drinkable temperature without having to reheat it, which can sometimes result in a reduction in the quality and taste of the coffee. They are often used in homes, offices, and other settings where people may need to have a hot cup of coffee available for an extended period of time.